1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has an improved insulation structure disposed on a substrate between driving electrodes to insulate them from each other.
2. Description of Related Art
Generally, electron emission devices are classified into those using hot cathodes as the electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a surface-conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
The MIM-type electron emission device has an election emission region with a metal-insulator-metal (MIM) structure, and the MIS-type electron emission device has an electron emission region with a metal-insulator-semiconductor (MIS) structure. When voltages are applied to the two metals or the metal and the semiconductor on either side of the insulator, electrons migrate from the high electric potential metal or semiconductor to the low electric potential metal, and are accelerated.
The SCE-type electron emission device includes first and second electrodes formed on a substrate while facing each other, and a conductive thin film disposed between the first and the second electrodes. Micro-cracks are made at the conductive thin film to form electron emission regions. When voltages are applied to the electrodes while making the electric current flow to the surface of the conductive thin film, electrons are emitted from the electron emission regions.
The FEA-type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the material due to the electric field in a vacuum atmosphere. A front sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a layer formed with a carbonaceous material, such as carbon nanotube, graphite and/or diamond-like carbon, has been developed to be used as an electron emission region of the FEA-type electron emission device.
Although the electron emission devices are differentiated in their specific structure depending upon the types thereof, they all basically have first and second substrates forming a vacuum vessel (or a vacuum chamber). Electron emission regions are formed on the first substrate together with driving electrodes for controlling the electron emission of the electron emission regions. Phosphor layers are formed on the second substrate together with an anode electrode for effectively accelerating the electrons emitted from the first substrate toward the phosphor layers to thereby emit light and/or display an image.
With the FEA-type electron emission device, cathode and gate electrodes are formed on the first substrate as the driving electrodes. The cathode electrodes are electrically connected to the electron emission regions to supply electric currents to the electron emission regions. Electric fields are formed around the electron emission regions using a voltage difference between the gate electrodes and the cathode electrodes, thereby inducing the electron emission. The cathode and gate electrodes are insulated from each other by an insulating layer disposed therebetween.
With the FEA-type electron emission device, the insulating layer may be formed either with a thickness of 1 μm or less using a process referred to as a thin film process, such as a deposition process; or with a thickness of 1 μm or more using a process referred to as a thick film process, such as a screen printing process, a doctor blade process, and/or a laminating process.
In the thin film process case, a micro-pixel may be easily formed. However, with the thin insulating layer formed through the thin film process, as the height of the gate electrodes with respect to the electron emission regions is lowered (due the thinness of the insulating layer formed through the thin film process), an electric field due to a high voltage applied to the anode electrode (referred to hereinafter simply as an anode electric field) may directly influence the electron emission regions.
Accordingly, in the above thin film process case, electrons may be emitted from the electron emission regions to pixels that should have been turned off with the driving of the electron emission device due to the influence of the anode electric field, thereby emitting unwanted light through the phosphor layers of the pixels. Consequently, in the electron emission device with the thin insulating layer formed through the thin film process, a high voltage should not be applied to the anode electrode, thereby limiting the intensity of a screen luminance.
In the thick film process case, the gate electrodes may be formed at a plane higher than the electron emission regions to thereby reduce the spread of electron beams so that the mis-operation of the device due to the anode electric field can be prevented, but the thick insulating layer formed through the thick film process can result in the formation of a parasitic capacitance between the cathode electrodes and the gate electrodes due to the high dielectric constant of the insulating layer. Therefore, in the electron emission device with the thick insulating layer, the driving signals can be easily distorted due to the parasitic capacitance of the thick insulating layer so that it becomes difficult to correctly drive the respective pixels.